searchable, to find what a term means on various projects or see possible synonyms (linked)

translatable, to have a maximal adaptability

general and specific, to see all possible terms, or just terms about a specific topic.

A term has one to many definitions
A term has zero to many synonyms
A term has zero to many language equivalents (not translations but terms matching the same definition in an other language)
A definition is linked to one to more project (extensions)

A term has zero to many translations
Synonyms have zero to many translations or have zero to many language equivalents
A definition has zero to many translations

A user may want to search for a term, a translation, a synonym or a group of terms linked to a project. For example, I want to see what "Topic" means, if "Sujet" is a synonym of something or all definitions linked to Flow.

The pro is that it is far more flexible regarding the data rendering. The con is that I have no idea how hard this would be to manage such a structure within the translation extension, I don't think it is treatable as is with the current state of the extension.

Sure, but would such an approach be adopted this is not the form most users would consult the glossary, it just make it more structured with all the pro and cons of such an approach. Just like wikidata in fact.